Seems to work fine. KDE crashes occasionally, but that might be unrelated to running it on POWER9. Works fine as a KVM host via virt-manager (tested with Debian 10 as the guest). Be warned that the installer will enable the contrib repos (without your knowledge or consent), which is bad from a software freedom standpoint.

Seems to work fine with KDE. Default version of Linux works fine. Be warned that the installer will enable the contrib repos (without your knowledge or consent), which is bad from a software freedom standpoint. However, running dpkg-query -W -f='${Section}\t${Package}\n' | grep ^contrib (see this Stack Exchange answer) suggests that no actual packages from the contrib repos are installed by default, so you should be able to disable the contrib repos after installation without ever being exposed to contrib-packaged software.